Author
Topic: Loctite (Read 2076 times)

I have searched the forums and found some information on loctite, but I am left wondering how suitable it is for bonding a built up crank shaft for a small 1/2in bore twin steam engine I am building. Loctite 609 has a shear strength of 2300psi, while tin solder has between 2000 and 4000psi. Not sure if I should solder it or use the loctite. It would be much easier to just glue it together. What do you think?

Your suggestions worked great. The webs were a very close fit on the center shaft and crank pins. I cleaned everything with lacquer thinner added loctite and stuck it together. Waited 24hrs and pinned all of the joints with .0625in hard wire pins. Thank you!!

WW11 British mechanical gun computers with hundreds of miniature gears and wheels used Standard 1:48 Tapered pins Size 7/0 which is 0.0625" diameter large end, however in a engineering working life have not come across "Hard Wire Pins" or how they are inserted and used

The pins were made from some .0625 inch diameter wire I had laying about. It was very hard to cut and if it is bent sharply it breaks. Just kind of made up the “hard wire pins” thing sounded good at the time. Not very technical but it seemed to be good for the job. After reading your post and doing a bit of reading i now see that a tapered pin would have been more appropriate for the job. I am not a machinist by trade and am having a lot of fun learning new things. Thank you

I use #638 Loctite on everything. It is the only Loctite I use. It works great for assembling small crankshaft, and as an added locking feature, I wait 24 hours for the Loctite to cure, then drill and pin the joints with a piece of 1/16" music wire, which has been (of course) dipped in Loctite before being pushed (not pressed) into place. have never used tapered pins.---Brian

I use #638 Loctite on everything. It is the only Loctite I use. It works great for assembling small crankshaft, and as an added locking feature, I wait 24 hours for the Loctite to cure, then drill and pin the joints with a piece of 1/16" music wire, which has been (of course) dipped in Loctite before being pushed (not pressed) into place. have never used tapered pins.---Brian

Brian, I have been using the 603 retaining compound with good results. Just looked up the 638, sounds similar but can handle bigger gaps than 603? Is the 638 watery or thicker, like the Red?

Hi Chris ,i have just used some 638 on my flywheel as the key disappeared in transit ..It is very gloopy and dark green and takes about 1/2 hour to start to set then the longer the better to cure. it takes quite a while to start to set so gives ample time to position..... willy

Hi Chris ,i have just used some 638 on my flywheel as the key disappeared in transit ..It is very gloopy and dark green and takes about 1/2 hour to start to set then the longer the better to cure. it takes quite a while to start to set so gives ample time to position..... willy

Great - thanks! The 603 is quite thin, so it needs a tighter joint, and grabs pretty quickly. Nice to know the difference, times when each would be better.

After thinking about this topic, a bit more I decided to look at it as an engineer would, probably should have started with this. The cured compressive shear strength of Loctite 609 after 24hrs is 2290psi. The crank shaft to crank web joint is in shear because the shaft wants to rotate in the web.

The shaft is .250dia and the web is .125in thick so the total area of the joint is:

The total strain the joint can resist is the area * the compression shear strength of the bonding material:.0981in*2290psi=224.649In/lbs

Or: (224.649In/lbs)/12=18.720ft/lbs

Really quite a lot when you think about the size of the parts and the application. Tin based soft solder has about the same shear strength. Of course, this is the ideal condition, assuming a good fit and clean parts. Loctite 680 has an even higher shear strength at 3500psi after 24hrs. Loctite 638 has a final cure shear strength of 4200psi on steel after 7days. Despite what the engineering says I still put my trust in experience, again, thank you for your help. Amazingly strong sticky stuff.

Unfortunately Henkel [the German owned producer of the Loctite products] has inherited and maintained the crazy scenario of having different Loctite codes for the same Product as marketed in different Countries

This together with a product range that far exceeds the needs of a model engineers $ budget

I have long stopped using their Aerosol Primer T and have substituted a refillable plastic pump bottle of Isoprop Alcohol.....

So for structural joints I use Loctite Grade 680, and for for demountable [with hand tools].....the Grade of 243 which listed as a Thread Locker

Derek

PS...I did a similar back check after reading your post however based this on pin diameter and web thickness of 0.1875" and this resulted on 165.5"/pounds shear...I too am am not yet converted to being a believer of Loctite for small diameter work, so fully agree with the backup of the pins...although Size 7/0 Taper pins would have been my first choice

Hard to describe the viscosity of something in print. It is thicker than the red Loctite I have seen. About like corn syrup on a warm day. It flows well, sets up fast but really needs 24 hours before it reaches full strength.---Brian

If you use primer n anaerobic lockers will set up a whole lot faster and stronger. Plus it you use loctite on bushings, pins and other thing normally pressed it you will get a stronger than press fit with a nice slip fit with loctite and primer n. The shear strength is stronger than what a press fit is.

If you use primer n anaerobic lockers will set up a whole lot faster and stronger. Plus it you use loctite on bushings, pins and other thing normally pressed it you will get a stronger than press fit with a nice slip fit with loctite and primer n. The shear strength is stronger than what a press fit is.

Correct. I always use Loctite primer, especially on none reactive materials such as aluminum.